As means for improving properties and, specifically, gas-barrier property of various plastic base materials, there has been known an art of forming an inorganic barrier layer of a silicon oxide or the like by vacuum evaporation on the surfaces of the plastic base materials (patent document 1).
In the applications of various electronic devices that have been developed and put into practice in recent years, such as organic electroluminescent (organic EL) devices, solar cells, touch panels, e-papers and the like, that must avoid leakage of the electric charges, it is a requirement to impart a high degree of water-barrier property to the plastic base materials forming the circuit boards or to the plastic base materials such as films sealing the circuit boards. However, the inorganic barrier layer formed as described above is not capable of meeting the requirement for attaining water-barrier property of a high level. Therefore, a variety of proposals have been made for improving water-barrier property.
A patent document 2, for example, proposes a gas-barrier laminate comprising an inorganic barrier layer formed on the surface of a plastic base material, and a sealing layer formed on the inorganic barrier layer, the sealing layer being dispersed with nanoparticles of a metal oxide or carbon nanotubes as a moisture-absorbing agent.
A patent document 3 proposes a gas-barrier laminate (film) comprising an inorganic barrier layer, an organic layer and a water-trapping layer formed on a base film, the water-trapping layer being formed of a moisture-absorbing polymer (concretely, a polyamide) or being formed by dispersing a moisture-absorbing material such as silica gel or aluminum oxide in a high molecular binder such as a resin that can be cured with electron rays or ultraviolet rays.
Further, a patent document 4 proposes a gas-barrier laminate comprising a gas-barrier film and a moisture-absorbing layer formed by vacuum evaporation on the surface of a plastic base material, the moisture-absorbing layer containing an alkylene oxide, acrylate nanoparticles or an organometal complex.
However, the gas-barrier laminates proposed by the above patent documents 2 to 4 are not, either, capable of attaining high degrees of water-barrier property. To attain a super-barrier property against water having a water vapor permeability of, for example, not more than 10−5 g/m2/day, it becomes necessary to employ a layer structure that includes many layers (moisture-absorbing layers or sealing layers) for absorbing moisture. As a result, a lot of laborious work is needed for forming a multi-layered structure causing a decrease in the productivity. Therefore, it has been desired to further improve water-barrier properties. Besides, there still remains a problem in that upon absorbing the moisture, the layers (moisture-absorbing layers or sealing layers) undergo swelling and lose dimensional stability. Therefore, it has been urged to provide a moisture-absorbing layer that is capable of exhibiting excellent moisture-absorbing capability over extended periods of time for also realizing super-barrier property using the layers of a number as small as possible.
To meet the above requirements, the present applicant has previously proposed a gas-barrier laminate having a water-trapping layer in which a specific granular moisture-absorbing agent was dispersed in the matrix of an ionic polymer, the water-trapping layer being formed on an inorganic barrier layer on a plastic base material (patent document 5). In the gas-barrier laminate proposed here, the water-trapping layer effectively traps water. Therefore, the gas-barrier laminate not only exhibit very excellent water barrier capability but also effectively suppresses the water-trapping layer from swelling despite of having absorbed moisture. Therefore, super-barrier property against water is realized with the layers of a number as small as possible, and favorable dimensional stability is also attained.
However, the above gas-barrier laminate is still accompanied by such a problem that the water-trapping layer easily loses its activity. Therefore, it has been urged to maintain excellent properties for extended periods of time with stability.